title: Constitutive, agonist-accelerated, recycling and lysosomal degradation of GABA(B) receptors in cortical neurons.
abstract: Endocytosis is considered as an important mechanism for regulating cell surface numbers and thereby signaling strength of G protein-coupled receptors. Currently, little is known about the endocytotic pathways of GABA(B) receptors in neurons. Here we report that GABA(B) receptors are constitutively internalized presumably via clathrin-dependent endocytosis in cultured cortical neurons. Colocalization of GABA(B) receptors with endosomal marker proteins indicated sorting of GABA(B) receptors from early endosomes to recycling endosomes and to lysosomes. Cell surface biotinylation experiments revealed fast constitutive recycling of GABA(B) receptors as the predominant pathway that was accelerated by the GABA(B) receptor agonist baclofen. Finally, degradation of GABA(B) receptors in lysosomes was demonstrated by their intracellular accumulation upon inhibition of lysosomal proteases and by blocking recycling which resulted in the redirection of receptors to lysosomes for degradation. These data imply rapid constitutive - agonist-accelerated - recycling of GABA(B) receptors presumably via clathrin-coated pits and their final targeting to lysosomes for degradation.
authors.affiliation: Institute of Pharmacology and Toxicology, University of Zürich, Winterthurerstrasse 190, 8057 Zürich, Switzerland.
authors.forename: Thomas
authors.initials: T
authors.lastname: Grampp
authors.forename: Valerie
authors.initials: V
authors.lastname: Notz
authors.forename: Ilja
authors.initials: I
authors.lastname: Broll
authors.forename: Natalie
authors.initials: N
authors.lastname: Fischer
authors.forename: Dietmar
authors.initials: D
authors.lastname: Benke
mesh_terms: D000818:Animals; D001418:Baclofen / Q000378:metabolism; D015415:Biomarkers / Q000378:metabolism; D002460:Cell Line; D002478:Cells, Cultured; D002540:Cerebral Cortex / Q000166:cytology* / Q000378:metabolism; D002966:Clathrin / Q000378:metabolism; D015853:Cysteine Proteinase Inhibitors / Q000378:metabolism; D004705:Endocytosis / Q000502:physiology*; D011992:Endosomes / Q000378:metabolism; D005260:Female; D018755:GABA Agonists / Q000378:metabolism; D058786:GABA-B Receptor Agonists; D006801:Humans; D007476:Ionophores / Q000378:metabolism; D007976:Leupeptins / Q000378:metabolism; D008247:Lysosomes / Q000378:metabolism*; D008985:Monensin / Q000378:metabolism; D009474:Neurons / Q000166:cytology / Q000378:metabolism*; D011247:Pregnancy; D051381:Rats; D017208:Rats, Wistar; D018080:Receptors, GABA-B / Q000378:metabolism
chemical_list: D015415:Biomarkers; D002966:Clathrin; D015853:Cysteine Proteinase Inhibitors; D018755:GABA Agonists; D058786:GABA-B Receptor Agonists; D007476:Ionophores; D007976:Leupeptins; D018080:Receptors, GABA-B; D008985:Monensin; D001418:Baclofen; C032854:leupeptin